This invention relates to a clamping nosepiece for machines which perform Rockwell hardness tests.
Rockwell hardness tests are performed on various workpieces to determine their hardness. Such machines generally comprise a C-shaped frame with a vertically adjustable anvil projecting upwardly from the bottom of the machine on which the workpiece sits.
A penetrator, often diamond, is attached to the head or top of the machine and after suitable preparation, the penetrator penetrates into the workpiece held on the anvil under application of the "major load". The depth of penetration is related to the hardness of the material being tested.
In order to ensure accuracy in the testing procedure, it is necessary to hold the workpiece steady while the major load is applied. In some cases, this is done by an operator manually holding the workpiece and using the diamond penetrator to bear on the top of the workpiece sufficiently to hold it in place. The approach is not satisfactory because the operator can not ensure against movement during the test, the workpiece may not be rigidly held in place and using the penetrator to hold the workpiece down introduces its own error into the process. Although the holding force required for certain operations can be accommodated manually, in other cases it cannot.
One approach to providing a clamping nosepiece is identified in U.S. Pat. No. 2,804,769 issued to C. W. Clark, Sr. entitled "Hardness Tester Work Piece Clamping Means". That patent describes a clamp which includes a collar 41 to bear against the workpiece 25 supported on an anvil 11. The collar 41 is part of a nose piece assembly comprising a tube 43 and flange member 46 which are fixedly connected to the head of the machine as shown at 47. A compression spring 42 has one end bearing against the top of collar 41 and the other end bearing against the bottom of the housing. The tension in the spring is controlled at the top by rotating tube 43 in flange 46 to adjust the pressure bearing against the top of the spring. One disadvantage of the Clark system is that the nosepiece is fixedly connected to the head of the tester.
Since there are many cases when a clamp is not required, such a fixed connection limits the versatility of the machine. Another problem is that the manner in which the compression spring bears against the collar 41 leads to inaccuracies in conducting measurements. This is due to the limited force which can be brought to bear on the small bearing surface of the collar on which the spring rests. Therefore, a slight tilting in the workpiece may not be properly compensated since the pressure may not be enough to force the surface of the workpiece to be so-oriented so as to be exactly perpendicular to the movement of the penetrator. Another problem of the Clark device is that the positional relationship between the tip of the penetrator and that of the collar is not adjustable. This can present problems since all diamond needles are not exactly the same size. Still further, it is preferable to be able to vary the force of the clamp on the workpiece prior to applying the minor load. This will allow for varying the clamping force by using the clamp rather than using the penetrator movement to vary the force. Another problem associated with the Clark device is that movement of the clamp with respect to the penetrator is through relative frictional movement between collar 41 and tube 43. Repeated up-down movement of these members results in a frictional hysteresis which can affect the actual hardness test measurements.
U.S. Pat. No. 3,877,298 was issued on Apr. 15, 1975 to Rajendra K. Narang and is entitled "Workpiece Clamp and Tool Shielding Device and Combination Thereof With a Tool Applying Apparatus". That clamp represented an improvement over the Clark system in that the clamp nose was removable from the head by using a pair of manually operating clamping screws which connect the clamping nose assembly to the head of the machine. Additionally, the Narang system provides a wide compression spring 27 bearing against a wide flange 21, the wide flange being formed as part of sleeve 20. Narang posits that the wide flange eliminates rocking or cocking of the sleeve on the workpiece, which it stated to be an advantage over the prior art. The other problems associated with the prior art are not recognized or addressed by the Narang system. Additionally, use of the widened flange 21, while allegedly providing benefits also causes the Narang system to be unwieldly.
An object of the present invention is to provide a clamping nosepiece which is compact in design.
Another object of the present invention is to provide such a nosepiece which is removable from the head of the tester.
Still another object of the present invention is to provide such a nosepiece in which the amount of holding force on the workpiece can be adjusted.
Another object of the present invention is to provide such a nosepiece in which the position of the penetrator with respect to the clamp is adjustable.
Yet another object of the present invention is to provide such a clamping nosepiece in which the deleterious affects of frictional hysteresis are substantially eliminated.
Another object of the present invention is to provide such a nosepiece which securely clamps the workpiece so that rocking or cocking of the workpiece is prevented.
Still another object of the present invention is to provide such a nosepiece in which adjustments can be made for different sized penetrators to eliminate their breaking.
Other objects, advantages and features of the invention will become more apparent thereinafter.